1. Field of the Invention
The present invention relates to a top-emission organic electroluminescent display having a metal-silicide layer at an interface between a reflective layer and a transparent electrode layer to prevent corrosion due to galvanic phenomena and to implement a high quality screen.
2. Description of the Related Art
A galvanic effect refers to a phenomenon that current flows between two adjacent dissimilar metals because of a voltage generated by a potential difference between the metals, thereby producing electricity therein. In the two dissimilar metals coming into electrical contact with each other in this way, one metal having high activity (i.e., with low potential) acts as a positive electrode, and the other metal having relatively low activity (i.e., with high potential) acts as a negative electrode by a difference of work functions at an interface of the dissimilar metals. At this time, when the two metals are exposed to a corrosive solution, the two metals are corroded due to the potential difference between the two metals. This phenomenon is called “Galvanic Corrosion” and, in the galvanic corrosion, the positive electrode having the high activity is rapidly corroded more than when it is used by itself, and the negative electrode having the low activity is corroded at a relatively slow speed.
A typical top-emission organic electroluminescent display includes a reflective electrode with good reflection properties at one side of the display. The reflective electrode is composed of conductive materials having a suitable work function as well as the good reflection properties. However, there is not yet a single suitable material satisfying all of the properties. Accordingly, the reflective electrode is generally made of a multi-layered structure including a reflective layer separately formed and an electrode material layer formed on a top surface of the reflective layer, the electrode material layer having conductivity different from that of the reflective layer. Therefore, when the typical top-emission organic electroluminescent display has the multi-layered structure, the galvanic corrosion phenomenon at the interface of the dissimilar metals cannot be ignored.
By way of example, FIG. 1 shows a partial cross-sectional view of a conventional top-emission organic electroluminescent display. Referring to FIG. 1, the top-emission organic electroluminescent display has a structure in which a reflective layer 110a and a transparent electrode layer 110b, which are used as a first electrode layer 110, are sequentially stacked on a substrate 100, and an organic layer 130 and a second electrode layer 140 are sequentially formed on the transparent electrode layer 110b. 
In the top-emission organic electroluminescent display having this structure, the reflective layer 110a is uniformly formed by a method such as sputtering or vacuum deposition of high-reflectivity metal materials. Conventionally, an active metal such as aluminum or aluminum alloy has been used as the reflective layer.
Subsequently, the transparent electrode layer 110b is formed by depositing a transparent electrode material on the reflective layer 110a, such that a light incident from the outside is reflected by the reflective layer 110a, and then the transparent electrode layer 110b is patterned to form the first electrode layer 110. In this process, indium tin oxide (ITO) or indium zinc oxide (IZO) is used as the transparent electrode material.
Finally, the top-emission organic electroluminescent display is completed by forming a pixel defining layer 120 which defines a pixel region, at both sides of the first electrode layer 110, and by forming the organic layer 130 having an emission layer and the charge (electron and hole) transporting capability, and the second electrode layer 140 on the pixel defining layer 120.
In the processes of fabricating the electroluminescent display as described above, patterning the first electrode layer 110 is typically performed by successive photolithography and etching processes. In detail, patterning the first electrode layer 110 includes forming a photoresist pattern on the transparent electrode layer 110b, performing a typical exposure and development process of the photoresist pattern, and sequentially etching the transparent electrode layer 110b and the reflective layer 110a using the photoresist pattern as a mask.
For example, typical wet or dry etching may be used as the above etching process. In case of the wet etching, a desired pattern is obtained by applying or spraying strong acid solutions such as HF, HNO3, H2SO4 to a region to be etched. Also, the strong acid chemical materials and strong base chemical materials such as HNO3, HCl, H3PO4, H2O2, and NH4OH are used for cleaning and strip processes after the etching process.
The strong acid chemical materials and the strong base chemical materials, which are used in the etching, cleaning and strip processes, are directly contacted to the transparent electrode layer 110b and the reflective layer 110a used as the first electrode layer 110. Accordingly, as shown in FIG. 2, the galvanic corrosion phenomenon occurs at the interface of the transparent electrode layer 110b and the reflective layer 110a [J. E. A. M. van den Meerakker and W. R. ter Veen, J. Electrochem, Soc., vol. 139, no. 2, 385(1992)]. In particular, considering that a metal such as aluminum and alloys thereof used as the reflective layer is rapidly corroded and is likely to form a metal oxide layer 110c such as, for example, Al2O3, even when it is exposed to the air for a short time, there are serious problems that the metal oxide layer 110c is generated through the galvanic corrosion phenomenon. In particular, when the chemical material partially remains at the interface between the transparent electrode layer 110b and the reflective layer 110a, the corrosion through the galvanic corrosion phenomenon is accelerated, and a crevice corrosion in which the corrosion proceeds at certain areas occurs.
Such a galvanic corrosion phenomenon is propagated along the interface between the transparent electrode layer 110b and the reflective layer 110a. Therefore, contact resistance between the layers is rapidly increased, and very unstable resistance distribution is created. As a result, in the conventional top-emission organic electroluminescent display, a brightness non-uniformity is generated in which some pixels appear brighter while other pixels appear darker when the display is turned on, which leads to the degradation of display quality.
To solve such a galvanic corrosion problem, U.S. Pat. No. 6,387,600 assigned to Micron Technology, Inc. discloses a method for preventing the galvanic corrosion at the interface of aluminum and ITO made of a transparent electrode material. Specifically, the patent discloses a method of forming a passivation layer such as chromium, chrome alloys, nickel, or cobalt stacked on an aluminum layer, to prevent corrosion caused by chemical materials in a photolithography process, an etching process and a patterning process. However, the passivation layer used in the above patent is removed by an etching process after the patterning process is completed. In this etching process, a mixed etchant of ceric ammonium nitrate and acetic acid is used, and therefore, the galvanic corrosion may take place again.
In view of the above, a clear solution to suppress the galvanic corrosion on the aluminum reflective layer of the top-emission organic electroluminescent display is still needed.